Benign prostatic hypertrophy (BPH) occurs in most men over the age of forty and causes clinical problems in a significant percentage of all such individuals. BPH often results in obstructive symptoms which can lead to bladder decompensation that may culminate in urinary retention. Elderly or debilitated patients with BPH often have multiple medical problems which may preclude surgical removal of the bladder outlet obstruction as a viable option. Currently, these patients often require long-term indwelling bladder catheterization, which may lead to multiple problems, including urinary tract infection and sepsis, epididymitis, bladder stones and bladder cancer.
The surgical treatment of BPH has been routine for many years. One method of surgical treatment is open prostatectomy whereby an incision is made to expose the enlarged prostate gland. The hypertrophied tissue is removed under direct vision. Another method, which has gained increasing usage in recent years, is transurethral resection. In this procedure, an instrument called a resectoscope is placed into the external opening of the urethra and an electrosurgical loop is used to carve away sections of the prostate gland from within the prostatic urethra under endoscopic vision. See Benign Prostatic Hypertrophy, edited by Frank Hinman, M.D. and particularly the chapter entitled "Prostatectomy, Past and Present" by Geoffrey D. Chisholm, M.D.
Notwithstanding the significant improvement in patient care resulting from the widespread application of transurethral resection, there remains a need for less invasive methods of treating the symptoms of prostatic enlargement. Various complications including impotence, incontinence, bleeding, infection, residual urethral obstruction, urethral stricture, and retrograde ejaculation may affect the patient following transurethral resection.
One of the earliest applied methods of relieving the acute urinary retention symptomatic of prostate enlargement was the placement of a catheter through the external urethral opening into the bladder thereby allowing the outflow of urine from the bladder by way of the catheter lumen. Such urinary catheters typically employ a balloon at the tip which, when inflated, prevents the expulsion of the catheter from the body. Although this method is effective in achieving urinary outflow, it is generally unacceptable as a long term treatment due to problems of infection and interference with sexual activity. In addition, such patents require close monitoring and frequent catheter changes. This results in great inconvenience to the patient and high medical costs.
The use of dilating bougies and sounds for mechanical dilation of the prostatic urethra have been attempted without success in the treatment of BPH. The fibrous and muscular tissue of the prostate gland rebounds after dilation, resulting in only a temporary reduction of urethral constriction.
A method of treating prostate disease involving the application of balloon dilation in a similar manner as in percutaneous transluminal angioplasty of arterial occlusions has been proposed in an article in the September 1984 issue of Radiology, page 655 entitled "Prostatic Hyperplasia: Radiological Intervention" by H. Joachim Burhenne, M.D., et al. This method of prostate dilation can be expected to have only a short term alleviation of urinary retention as the fibrous and resilient hypertrophied prostate gland will in a relatively short period of time cause the constriction of the prostatic urethra to recur. Also in the angioplasty arts, Palmaz, et al. have described the percutaneous, sheathed insertion of an expandable endoprosthesis into various major arteries of dogs in the article "Expandable Intraluminal Graft: A Preliminary Study" in the July 1985 issue of Radiology at page 73.
Finally, over the past decade, various alternative surgical and non-surgical therapeutic treatments for BPH have been developed. These include medical therapy (anti-androgens, alpha-blockers, 5-alpha reductase inhibitors), ultrasonic aspiration of the prostate, transurethral incision, cryosurgery and hyperthermia.
A most promising alternative in the treatment of BPH has been the introduction and use of prostatic stents. A prostatic stent or spiral was first described by K. W. Fabian in Urologe (1980). There have been many subsequent develoments including the Prostakath.RTM. (developed by Engineers and Doctors A/S, Copenhagen, Denmark). This stent, which is a helical coil or spiral composed of stainless steel, is coated with 24 karat gold, which aids in preventing encrustation. The straight portion remains in the prostatic urethra while the distal portion remains in the bulbar urethra.
Another currently available stent is the UroLume Wallstent manufactured by American Medical Systems. This stent is constructed from a biomedical super alloy prosthesis woven in a tubular mesh and produced in various diameters and lengths. This stent is preloaded in a delivery system that allows direct visualization with the prosthesis and the urethra throughout the entire insertion procedure.
A number of patents directed to prostatic stents have also issued. U.S. Pat. No. 4,893,623 discloses a tubular stent having a plurality of passages comprising a first plurality of parallel filaments which are aligned at a diagonal to a second plurality of parallel filaments. The stent disclosed in U.S. Pat. No. 4,893,623 is formed from a single piece of material, such as a malleable biological compatible metal, and is designed to hold its expanded configuration under stress exerted by a hypertrophied prostate gland. See also U.S. Pat. No. 4,762,128. The stent disclosed in this patent is similar to the Urolume Wallstent. See "Prostatic Stents", Current Surgical Techniques in Urology, Kaplan and Koo (1990).
U.S. Pat. No. 4,994,066 also discloses a stent for treating BPH. The stent has a cylindrical conduit having a conical flange on one end and an annular flange on the other. The stent is constructed of a medical grade elastomer which is compressed for implantation and can thereafter be left for extended periods of time.
Finally, U.S. Pat. No. 4,955,859 discloses a high-friction prostatic stent. The stent includes a textured fabric layer for frictionally engaging the urethral walls to anchor the device within the prostatic urethra and to prevent migration back into the bladder or down the urethra.
Each of these stents have several problems associated therewith. Initially, stents such as disclosed in U.S. Pat. Nos. 4,893,623 and 4,955,859 can dig into surrounding tissue of the prostate, thereby leading to discomfort, inflammation and infection. As the stent of U.S. Pat. No. 4,893,623 expands, the perforations become larger and greater pressure is exerted between the expanded stent and the enlarged prostate. Under such conditions, the tissue of the urethral walls attempts to penetrate even more deeply into the perforations of the stent and thereby render the stent difficult, if not impossible, to remove without major surgery. Further, stents such as disclosed in U.S. Pat. No. 4,893,623 must be inserted using complex and specialized apparatus.
The Prostakath.RTM., identified above, has not gained widespread acceptance, because of concerns regarding encrustation of the metal spiral which may cause the spiral to adhere to the urethral walls, thereby necessitating surgery to remove the device. There have been further reservations that the tip of the spring may cause bladder irritation, and further concerns that attempts to remove the metal spiral by endoscopically pulling on its distal end may cause the spiral to unwind such that the sharp end of the wire lacerates the urethra. Finally, this stent has also experienced migration and may cause incontinence.
In addition, some prior art stents have typically lacked sufficient flexibility and may be difficult to use with patients having unusual or abnormally shaped prostatic lobes. Some prior art stents have also been expensive to fabricate.
It would be desirable to provide a prostatic stent which can accommodate prostates having different lengths, widths and shapes. Such a stent could be constructed from a tubing material of the type long successfully utilized in ureteral stents and catheters.
It would be further desirable to have a prostatic urethral stent which would not become incorporated into the tissues of the prostate, as is characterized by wire-mesh stents.
It is thus an object of the present invention to provide a novel prostatic stent constructed from tubing of the type used in ureteral stents and catheters and which improves over prior art prostatic stents.
It is still a further object of the present invention to provide a prostatic stent which will not become easily dislodged or migrate.
It is yet a further object of the present invention to provide a prostatic stent which can be easily inserted and removed without open surgical intervention.
It is still yet an additional object of the present invention to provide a prostatic stent which is less irritating to the urethra and does not interfere with urinary continence.
These and other objects of the present invention will become apparent from the summary and detailed description which follow.